The present invention relates to a device for electrical signal generating systems, and particularly to a device and method for visually modelling cardiac waveforms for demonstration or teaching purposes.
Although normal contraction of the heart is commonly referred to as a "heartbeat," in actuality each such "beat" is a muscular wave that travels across the surface of the heart. It should further be understood that there are two components to a "heartbeat," one being electrical, the other muscular. A typical heart contraction normally originates from an area in the upper right atrium (the sinus auricular node) and spreads in the form of a depolarization wave through the atrioventricular node across the heart to the ventricular myocardium. This depolarization wave then spreads through the muscular tissue of the ventricle to cause the ventricle to contract for pumping blood through the arteries. Electrical activity inherent to the individual myocardial cells initiates and sustains the depolarization wave.
In the event that various cells within the heart have been damaged, propagation of the depolarization wave across the heart may be obstructed. Furthermore, in the event that the cells in a specific region of the heart have been damaged, conflicting depolarization-waves may be generated by the affected cells, which interfere with the normal heart rhythm. A condition known as cardiac arrhythmia or dysrhythmia results.
Medical treatment of cardiac irregularities may be facilitated by an understanding of the mechanisms of cardiac electrical impulses. Such an understanding may be gained through a precise description of the structure and function of the cardiac tissues and electrical pathways. To this end, advances in medical technology have resulted in development of various devices for simulating various electrophysiological impulses. For example, U.S. Pat. No. 3,323,068 to woods purports to teach an electrocardiogram (EKG) simulator for generating EKG waveforms of the human heart. Similarly, U.S. Pat. No. 3,469,115 to Cartridge purports to teach a cardiac waveform simulator for generating a pulse having a generally triangular shape and a rise time to fall time characteristic closely resembling the pulses of a human cardiac waveform. Both of these references relate to systems for generating analog signals representative of electrophysiological activity in a single dimension with respect to time.
More information on the general state of the art in cardiac mapping systems may be had by reference to Lebron et al., U.S. Pat. No. 5,041,973, the disclosure of which is herein incorporated by reference. The Lebron et al. reference purports to disclose a cardiac mapping system simulator for simulating a series of signals which represent two-dimensional (2D) electrophysiological (EP) impulses. Microprocessor circuitry is included for generating a 2D pattern of timed simulated EP impulses for application to an EP impulse display device, which comprises programmable circuitry for generating a succession of digital signals, and a circuit for receiving the digital signals and, in response, generating output signals on predetermined outputs thereof. The simulated pulses may be used to assess the proper functioning of cardiac mapping systems prior to their use on patients.
For demonstration or teaching purposes, it would be useful to directly and visually correlate a cardiac signal of known parameters with an EKG reading. None of the foregoing references teach a method or apparatus for visually displaying electrical impulses within a physical heart model and correlating those impulses to an EKG tracing on an external monitor. Thus, a need exists for apparatus that may generate heart waveforms and three-dimensionally model the resulting signals in the electrical pathways of a heart while simultaneously producing EKG tracings.